Efficient control and stall prevention in advanced configuration aircraft

ABSTRACT

Multiple initiatives are applied to achieve synergistic control enhancement and drag reduction benefits in an aircraft having independent airfoils producing downward force opposite to wing lift in normal flight, which are supported in specific wingtip locations. A method is disclosed teaching the exemplary stall resistance and control at high angles of attack demonstrated by preferred embodiments of the invention.

FIELD OF THE INVENTION

This invention relates to the field of aircraft; specifically to poweredand unpowered aircraft of all sizes, especially those operable at highlevels of aerodynamic efficiency; whether manned or unmanned; controlledor uncontrolled. The invention applies generally to design in fluiddynamic disciplines.

BACKGROUND OF THE INVENTION

Modern aircraft design recognizes conflicting priorities between higherspeed and lower speed operations. Aircraft for low speed flight differmarkedly from those intended for high speed flight, and one type mayrarely be useful for the other. Historically, to obtain higher speedrequires higher power, and high powered aircraft use a lot of fuel. Fastaircraft generally require long paved runways. Likewise, to shortentakeoff and landing distances, faster aircraft demand complex design,controls, and operation. Fast, but efficient aircraft-those having aminimum total of induced drag, surface drag (also known as friction dragor parasitic drag), and for supersonic aircraft, wave drag—also costmore because they are sensitive to size, weight, and incorporation ofall the mechanisms used to configure the aircraft for low speedoperation, such as when landing. This mandates more expensive design andmaterials. Comprehensive solutions targeting such problems at their mostfundamental levels are of great economic value, but until the present,to obtain lower drag in higher speed operation remains an expensiveprocess filled with compromise.

Two goals common to aircraft invention are the improvement of handling,especially at low speeds, and the reduction of drag. However, improvedhandling is frequently obtained at the cost of additional drag. Thus,aircraft types offering good handling at low speeds tend to have lowertop speeds. While reductions in drag allow a reduction in powerrequirements and fuel consumption, increases in available payload orrange, or corresponding reductions in weight, designers have to choosebetween the types of drag they can reduce, or accept both compromise andhigh costs. At low speeds, encountered during takeoff and landing andwhile maneuvering in airport traffic patterns, surface drag reductionsoffer little benefit. Indeed, highly streamlined aircraft frequentlyhandle poorly at low speeds and are further disadvantaged by the time ordistance needed to slow the vehicle down. At higher speeds, surface dragcaused by minor variations and imperfections becomes critical. On theother hand, lower induced drag greatly improves climb performance andpayload capacity for a given available power, improving range and fueleconomy well beyond whatever nominal savings are shown in cruisingflight. Lower air density at high altitudes rapidly demonstrates thevalue of designing for lower induced drag, because true airspeedsincrease in thinner air. Lower induced drag improves high altitudeflight, leading to benefits in high speed operation. This makes thereduction of induced drag significant for most aircraft, yet, aside fromsoaring applications, low induced drag is uncommon among low speedaircraft and rare among high speed aircraft. Thus a pressing need isimproved low speed handling in an aerodynamically clean aircraft alsohaving low induced drag.

According to both classical aerodynamic theory and experience,increasing wingspan lowers induced drag. However, all aircraft seekinggreater payload or economy through higher efficiency quickly reachlimits for material strengths and airport infrastructure, whichconstrain wingspan. Therefore, a goal of many aircraft designers is toobtain the induced drag reduction of greater wingspan by means oftechnology having similar effect. Unfortunately, many such efforts arenot practical. Some prior art lowers induced drag by marginal amounts,yet adds to total drag, weight, and complexity to such a degree thattheir net overall value is debatable. Simultaneous reduction of induceddrag and surface drag demands an entirely new approach.

Consequently, aircraft capable of high speed operation remain highpowered. They often require flaps, slats, or other high-drag means oflift augmentation even to operate at low speeds.

High costs of safely achieving such efficiency-promoting goals aslaminar flow and pressure seal of the aircraft flight surfaces mean thatfuselage drag remains the easiest target for compromise, and in atypical high speed aircraft, cabin volume is minimized. This negativelyimpacts the passenger experience and lowers utility. At the same time,efficiency losses of the smallest magnitude represent millions ofdollars in transportation fuel costs annually. Equivalent performance atlower fuel consumption is a need having extreme economic benefits.

Another goal of aircraft invention is greater safety. Crash prevention,short field and unimproved runway operation are objectives unfulfilledby the majority of prior art, especially among faster aircraft.Historically, stalls and stall/spins are the major cause of aircraftaccidents and are typically deadly when they occur in close proximity tothe ground or structures. A factor contributing to stall relatedaccidents is the erroneous belief that stall is a function of airspeed;that stalls do not happen above certain “speeds”. It does not help that“stall speed” is a term that permeates aviation, even though the correctunderstanding is widely known. Aircraft that do not stall thus oftenrepresent an ideal objective, but a rare reality. Likewise, improvementin air transportation systems require aircraft able to operate safely atboth lower and higher speeds than at present, such that safer futureaircraft may be defined in part by the smaller size of airports orprivate airfields needed to handle their operations. Growth in personalair vehicle initiatives is even more dependent upon safe low speedhandling characteristics, reduced noise, and improved ease of operation.Fast aircraft that can fly slowly while remaining fundamentallyincapable of departure from fully controlled flight thus represent a keyto distributed transportation solutions. For commercial aviation, at theother end of the size scale, dangerously powerful vortex created in thewake of very large transport aircraft represents both hazard andinefficiency. Invention that reduces wake vortex for fuel economy alsopromotes safer interaction of large planes with other aircraft.

Finally, practical roadable and stowable aircraft are needed. Newtechnology in aircraft design should give greater priority to removableand foldable flight surfaces to simplify ground transport and storage.Invention that builds from a base of simplicity, safety and efficiencyin these requirements leads the way to practical flying vehicles thatmay be drivable. Similar mechanical challenge is involved in variablegeometry wings. For both cases, simplified control paradigms and lightweight are paramount to overcoming the failures of prior art. Extensivestudy and research into these and the foregoing areas, including flightmodeling and scale model testing, has through insight resulted in theexemplary solutions embodied in the present invention.

BRIEF SUMMARY OF THE INVENTION

My invention applies multiple novel and counterintuitive initiatives toachieve outstanding benefits relating to aircraft efficiency andcontrol, which include a method for the prevention of stall. Theinvention characteristically positions separate and appropriatelysupported airfoils in the area surrounding the wingtip, verticallyspaced away from the generally affected airflow over the wing. Typicallyacting as enlarged aileron or elevon control surfaces, these airfoilsdiffer from ailerons of prior art not only by their larger separationfrom the wings, but also in their configuration to produce downwardforce, opposite to the direction of wing lift, in normal flight. Typicalaileron control surfaces (221, 227) found in the wings of conventionalaircraft (FIG. 22A) can be eliminated. When the airfoils are positionedbehind a center of wing lift that is behind the center of mass, thetypical horizontal control surfaces (220, 225), usually found centeredon the tail of conventional aircraft (FIG. 22A), can be eliminated. Theresulting configuration is extremely effective and allows the controlfunction of elevators (225, FIG. 22) and ailerons to be combined incontrollable elevons (9,10), which can provide simultaneous control oftwo or more rotational axes of the aircraft in preferred forms (FIG. 1).The significant downward aerodynamic force created by these relativelylarge, typically inverted airfoils (9,10) which are positioned,optimally, above and behind each wingtip area requires structureappropriate to reliably transfer pitch stabilizing forces and strongcontrol forces to the aircraft (FIG. 2) so as to preferably allow wingairfoils to be unbroken by hinge lines. External wingtip elevons (9,10)of a preferred embodiment (FIG. 1) may thereby be rotatably attached atboth ends so as to adjustably pivot on their spanwise axis. Upwardlyextending elevon support structure (7) may incorporate other functions,such as lateral (yaw) stabilizing functions. However, supportingstructure (5) at the wingtips need not be present in every embodiment,as its structural function may not always be necessary (FIG. 16B, FIG.15). In contrast to prior art, the detailed disclosure of variousenabling aspects of the invention, such as position, support,separation, span, orientation, and downward loading of generallyhorizontal control airfoils (9, 10) above or below the wingtip areateaches enhanced control authority and stability together with thereduction of complexity. Corresponding reductions in surface drag andweight may be achieved while simultaneously creating opportunity for amajor reduction of induced drag. The invention enables a lightweightstructure that may be more specifically configured to render theaircraft incapable of stall, by applying the disclosed method. Theinvention teaches many improvements, and they are combined to result ina new class of aircraft having outstanding capabilities andefficiencies. The exclusive invention claimed, though counterintuitiveand technically very advanced, is characterized by simplicity heretoforeelusive.

Applying the invention to new aircraft types solves many problemsimpeding aeronautical progress, particularly with respect to fuelefficiency. Application to existing types of aircraft results in a hugevariety of novel forms. Certain embodiments of this invention maysuperficially resemble biplane, boxplane or joined wing designs of priorart, but since the invention requires the upper or secondary flightsurfaces to produce downforce in normal flight, provide efficientcontrol of pitch and roll, and, optionally, allow their use in stallprevention, visual resemblance is misleading. In this disclosure, theterms structure, configuration, and structural configuration are usedinterchangeably in reference to the arrangement disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a preferred embodiment; a single enginegeneral aviation aircraft of high performance; capable of exceptionallow speed handling.

FIG. 2 is a view of said aircraft from the front.

FIG. 3 is a view of said aircraft from the top.

FIG. 4 is a view of said aircraft from the side.

FIG. 5 is a perspective view of a Very Large Transport aircraftembodiment.

FIG. 6 is a front view of the aircraft of FIG. 5.

FIG. 7 is a perspective view of an amphibious aircraft or seaplaneembodiment having also a hydrofoil embodiment.

FIG. 8 is a front view of the aircraft of FIG. 7.

FIG. 9 is a perspective view of a racing aircraft embodiment.

FIG. 10A is a perspective view of an aerobatic aircraft embodiment.

FIG. 10B is a front view of the aircraft of FIG. 10A.

FIG. 11 is a perspective view of a ducted fan propelled embodiment.

FIG. 12 is a perspective view of a twin engine business jet embodiment.

FIG. 13 is a perspective view of a multiple fuselage Very LargeTransport aircraft embodiment.

FIG. 14 is a perspective view of a fuselage-supported embodimentdifferent from a boxplane of prior art in that the full-span secondaryairfoils produce a downward aerodynamic force in flight.

FIG. 15 is a perspective view of a cantilever biplane-style embodimentdifferent from a canard or biplane of prior art in that the full-spansecondary airfoils produce a downward aerodynamic force in flight.

FIG. 16A is a perspective view of a twin engine aircraft embodiment.

FIG. 16B is a perspective view of an alternative embodiment of theaircraft of FIG. 16A.

FIG. 16C is a front view of the aircraft of FIG. 16B.

FIG. 17 is a perspective view of a blended wing body embodiment.

FIG. 18 is a front view of the aircraft of FIG. 1 at a high angle ofattack.

FIG. 19 is a front view of the aircraft of FIG. 1 at an angle of attacksufficient to illustrate the action of the method for preventing stall.

FIG. 20 is a section view of the aircraft of FIG. 3 showing the actionof the stall prevention method.

FIG. 21 is a perspective view of a sailplane embodiment.

FIG. 22A is a top view of a conventional aircraft of prior art.

FIG. 22B is perspective view of a canard aircraft of prior art.

FIG. 23 is a perspective view of the aircraft of FIG. 1 showing theaction of controls and the loading of flight surfaces.

A portion of the disclosure of this patent document contains materialwhich is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor the patent disclosure, as it appears in the Patent and TrademarkOffice patent file or records, but otherwise reserves all copyrightrights whatsoever.

DETAILED DESCRIPTION AND SUMMARY OF ADVANTAGES OF THE INVENTION

The invention disclosed is a fundamental enabling technology that may beembodied in various forms. Therefore, specific details disclosed hereinare not to be interpreted as limiting, but rather as a basis for theclaims and as a representative basis for teaching one skilled in the artto employ the present invention in virtually any appropriately detailedsystem, structure, or manner. The present invention applies toinnumerable aircraft designs including next (FIG. 5) and futuregeneration (FIG. 13) large transport aircraft, next generation generalaviation aircraft (FIG. 1), commuter aircraft (FIG. 16), blended wingbody aircraft (FIG. 17), Light Sport Aircraft (FIG. 15), personal airvehicles, remotely piloted vehicles (RPVs), unmanned aerial vehicles(UAVs), model aircraft, toy airplanes, and many others. Since theinvention can be readily adapted into products built by a majority ofaircraft manufacturers, using a variety of material processes, thetechnology is not disruptive. Aircraft configurations supporting large,highly separate external airfoils (9,10), preferably ailerons orelevons, so as to produce lift-opposing downforce in bilateral wingtiplocations (FIG. 1), by means of support structure able to reliablytransfer significant aerodynamic forces to the wing root (2), wing (4),or fuselage (1), whether through vertical stabilizers (7), cantilever(154) structure (FIG. 15), struts (152), fan ducts (111, FIG. 11),engine pylons (52, FIG. 5), rudders (142), boom structure (6), or otherbracing means, and/or to the wing tip area, via similar means (5, 143),simultaneously reduce drag and increase control. Many additionalbenefits are disclosed further herein. The extent to which thissynergistic combination of benefits occurs varies by objective and bythe degree to which one skilled in the art chooses to optimize his orher embodiment. However, in preferred embodiments, applying theinvention described results in extremely high levels of efficiency notfound in prior art.

The primary advantage of this invention is efficiency; not onlyaerodynamic efficiency but the enabling mechanical, structural,manufacturing, and economic efficiencies common to successful aircraftdesign. Defining this goal simply as the obtaining of a maximum ofbenefits at a minimum of costs, for aircraft designed under thisdisclosure, the major benefits offered by the invention comprise anextensive, interdependent list. These take the form of increased controlauthority; increased payload; lower lift-induced drag; lower surfacedrag; reduced power requirements; reduced fuel consumption; reducedcomplexity; reduced wingspan and tail height; reduced minimum speed;reduced weight; reduced runway length requirements; increased stability;increased structural strength and stiffness; increased top speed;increased cabin volume; increased control feedback; stall warning;prevention of stall; prevention of spin; coordinated turn behavior;improved aeroelastic dampening; and favorable center-of-mass excursionunder increasing payload. Preferred embodiments add improved pilotcomfort and workload reduction, efficient and favorable yaw coupling,enhanced visibility in all directions, short takeoff and landing (STOL)capability, large range of center of mass location, reduced noise,increased maximum altitude, high angle of attack maneuverability, andfully controlled, recoverable deep stall descent to this list.Significant reductions in drag, detailed herein, enable larger wingchords and greater wing area at a given span, which primarily lead tohigher lift capacity, slower landings, and greater ability to specifylarge cabin area. Optimum non-elliptical wing lift distributions can beexploited for additional gain. Simultaneous drag reduction, weightreduction, simplification, and control enhancement provides beneficialutility in many areas.

Corresponding reductions in cost may be viewed in several ways as well.To start, owing to the extreme simplicity of the wings (4) and controlsurfaces (9,10), which in a preferred embodiment (FIG. 1) comprise twoone-piece controllable airfoils (9,10) pivotably attached at their ends,costs due to manufacturing complexity and parts count are dramaticallyreduced. Indeed, the word “elevon” (9), the common term for a controlsurface combining the flight control functions (FIG. 22A) of theelevator (225) and the aileron (221), captures one such simplificationthat is enhanced, as disclosed (FIG. 1), by location and independencefrom wing airfoils, allowing the elimination of tail structure.

Testing of the invention has shown that the separate wingtip arrangementof independent aileron or elevon control surfaces (9,10) away from thedownward-deflected airflow over a wing provide efficient, responsivecontrol of aircraft without the weight and complexity of internalailerons (221), elevators (225), or, optionally, flaps (222) inconventional wings (FIG. 22). This control extends to low speeds andunusually high angles of attack. Although separate external ailerons(9,10) may thus be placed above or below the wing (4), as well as foreor aft, a significant improvement captured in all embodiments shownresults in separate ailerons (9,10) configured to produce downwardaerodynamic force (231), or negative lift, in normal flight, opposingthe lift (204) of the wings (4). Further teaching allowing eliminationof elevators places the ailerons (9,10) behind the center of lift,thereby making them elevons (9,10). Further teaching regarding thedisclosed method to obtain stall prevention refines their location tospecifically above and behind the outer portion of the wingspan, whichposition further minimizes induced drag. In best practice, the span ofthe surfaces providing downforce ranges between one-third of wingsemi-span and fully equal to wing semi-span.

Mechanical simplicity is central to the various embodiments illustratedfor safety and cost reasons. Especially are large commercial aircraftcosts improved by reducing the number and complexity of controlsurfaces. As mentioned, the elimination of outboard wing controls allowsthe entire wing (2,4) or its outboard portion (4) to be built to preciseairfoil geometries in one piece, without regard for the internalmechanics of a conventionally controlled wing; a major cost savings bothin manufacture and maintenance. Finally, widespread commercial adoptionof composite materials is enabled and accelerated by simple structuraldesign. Composites offer an indefinite lifespan that greatly exceedsthat of aluminum aircraft. The invention thus offers economy throughlower maintenance costs and extended service life in addition to savingsthrough energy efficiency.

Elimination of chordwise flow disruption caused by control surfacediscontinuities, such as seams (223), hinge lines (224), and controlsurface deflections on a traditional wing (FIG. 22) makes low surfacedrag an easily attained object of the invention. Low-drag airfoils ofthe laminar flow variety are often desired for high performanceaircraft. These airfoils frequently have a thin, highly loaded trailingedge that is challenging to articulate for control. Laminar flowairfoils are also typically sensitive to disruption; control surfacedeflection can cause adverse drag unlikely with other airfoils.

On a typical, conventional aircraft, (FIG. 22A) required movement of thecontrol surfaces breaks the designed airfoil at the hinge lines to varythe lift. For example, downward movement of the left aileron (221) addsadditional lift and drag to the left wing (226), while simultaneouslythe upward deflection of the right aileron (227) causes the right wing(228) to lose lift, and together the lift imbalance between the left andright wings causes the aircraft of this example to roll to the right. Asthe lift varies, so also does the drag. Imbalance in the drag of theleft and right wings—from the two oppositely deflected ailerons—may benegligible, or may sometimes provide a desirable amount of lateral yawin the direction of the turn. However, adverse yaw from roll inputremains a common problem in prior art; pursuit of low drag further addsto the challenge of avoiding it. In general, airfoil geometriesdisrupted by a hinged control surface break (224) do not maintain theirminimum predicted drag or allow highly reliable advance prediction oftheir characteristics in new designs. Further, should transition toturbulent airflow occur on a laminar flow wing, it is frequentlyaccompanied by an abrupt, major increase in drag. This possibilityamplifies any preexisting negative tendencies, and it can create themunexpectedly. Designers thereby face additional sensitivities that canproduce unwanted yaw, pitch, roll, or stall when pursuing low-dragand/or laminar flow features on conventional aircraft designs.

By contrast, using the present invention in a preferred manner (FIG. 1)allows every flight surface to be highly optimized for minimum surfacedrag, since the airfoils of the wings (4) and control surfaces (9,10)are unbroken. This allows the invention to directly improve high speedperformance, while simultaneously reducing the costs, weight, andcomplexity of construction. The large size and specific location of theelevons (9,10) create exceptional handling characteristics at both highand low speeds, while maintaining efficiencies in drag disclosed morefully herein, including such subtleties as a lack of wing pressureleakage due to absence of spanwise hinge gaps (223, 224). Behavior of adesign can be more reliably predicted in advance, as each surfacemaintains fidelity to the lift and drag properties of its airfoil.Rudder requirements are reduced due to absence of adverse yaw. As afurther advantage, flutter and other difficulties sometimes associatedwith all-flying (pivoting) airfoil structures (9,10) are readilyovercome in the invention by means of end supports and sweep. Naturally,the foregoing does not preclude the use of conventional controlsurfaces, or additional control surfaces, when so desired (FIG. 14), noris the invention limited to aircraft which are controllable, asfree-flight aircraft and aircraft having fixed surfaces are equallyimproved by the teaching. In some cases, the unusual degree of controland safety afforded by the invention at high angles of attack,particularly in application of the stall resistance method disclosedfollowing, allows reduction or elimination of flaps (222).

A key benefit of the invention is a major reduction of induced drag andits symptom, wake vortex, a spiral turbulence trailing the wingtips ofmost aircraft. Wingtip vortex is a huge problem unsolved in prior art.Vortex is created as a natural response to aircraft flight becausesuction from the mass of undisturbed air acts to efficiently equalizeand organize the three-dimensional fluid movements created by liftingsurfaces in motion, such as wings, which create a downwash in theirwake, when the disruption caused by such airflows persists over time.This suction powers the outward, lateral, spanwise flow known as the“vorticular flow” occurring at the wing, generally observable as astrong spiral flow (161) upon its departure from the wingtip (FIG. 16C).Vorticular flow has a cause. In the simplest terms, higher pressureunderneath lifting surfaces always tries to escape around the tip of thesurface to the low pressure side, and if the motion resulting from itsinitial success is strong enough and continues over time, anacceleration occurs forming a strong vortex (161) downstream of thewingtip. This vortex is a symptom and a primary measure of induced drag.Thus, quickly acting against the wing downwash and vorticular flows witha sufficient volume of air reduces the time required to reach downstreamequilibrium and the probability of vortex formation. This represents areduction in the total energy imparted by the aircraft to the air andthus a reduction in lift-induced drag.

In a 1988 paper entitled Viscous Induced Drag, Greene describes anentropy-based approach to calculating induced drag which validates howthe classically inadvisable, non-obvious design choices of theinvention, illustrated in various embodiments, such as low aspect-ratiowings (FIG. 10A) and wing sweep (FIG. 3), achieve their surprisingresults. This theory of induced drag, which indirectly focuses newattention on the role of viscosity and four-dimensional factors inamplifying the effects of spanwise momentum, predicts the development ofsubsequent novel aircraft forms and wing configurations. Yet, until thepresent, both the calculation of induced drag and the form of aircraftcapable of lowering it systematically have been mired in the legacy ofmodels with two-dimensional ancestry, which build upon priorwell-meaning simplifications with regard to the three-dimensionalmovement of air disturbed by an aircraft. However, a simple concept isall that is needed to discover the enabling principle of the inventionas respects induced drag reduction: moving a large volume of air in theopposite direction of the strong airflows that power vorticular flowhelps vortex to stabilize; or, more correctly, not form to a particularstrength.

Modern efforts to lower induced drag often attempt to impart acounter-rotational force to the vorticular flow, with limited success.Some prior art purports to break the vorticular flow into smallervortices, interfere with it, or destabilize it. However, smallstructures cannot move enough air without incurring major drag. Withoutadequate span or size of structures, or length over which to decelerateor interfere with vorticular flow, such efforts are severelydisadvantaged. Instead, the present invention utilizes, in preferredembodiments, enlarged horizontal elevons (9,10) that span typically 62%of the wing (2,4) semi-span above the outboard portions of the wings (4)(FIG. 3). Being separate, inverted airfoils of large span (FIG. 15),these easily impart the required negative lift without a major dragrise. Doing so behind the center of upward lift, they provide theaircraft positive pitch stability, and further impart an upward momentumto a large fluid mass of air, in opposition and interference to thedownwash caused by the wing (4). This opposing motion of air shouldoccur over a wide area at the maximum lateral extent of the wing orlifting body (4) to most effectively moderate the displacement ofairflow behind the aircraft, and can be used to add a counter-rotationalvector component (162) to the immediate streamwise flow of disturbed air(FIG. 16C). These opposing flows created by the negative loading andsubstantial vertical separation of the opposing airfoil structure (9,10)above or below the wingtip tend to decelerate, interfere with and absorbthe energies of wing (4) downwash powering vorticular flow (161). As aresult, induced drag drops by more than 40% in some embodiments (FIG.1). Such dramatically increased margin of drag reduction enables thepracticer of the invention to trade design priorities with greaterfreedom.

While a few rare aircraft configurations appear at first glance to besimilar to certain illustrated embodiments (FIG. 14 and FIG. 15), theinvention operates very differently from all prior art. Unlike joinedwing and boxwing designs which have large secondary wings providingpositive lift, as mentioned, in all embodiments of the invention thesecondary airfoils (141,154) do not contribute to the total upward liftof the aircraft; rather, they exert opposing, downward pressures (231)in the direction of gravity, in the same manner illustrated in theembodiment of FIG. 23. This condition is advantageously created in allembodiments by assuring that the aircraft center of gravity (203) isforward of the center of wing lift (204), establishing a positivepitching moment which must be counteracted by downforce provided by thesecondary, inverted airfoils (9,10, 141, 154). In this regard, theinvention is quite traditional.

On a typical aircraft of prior art, (FIG. 22A) greatest efficiency isobtained by locating the horizontal stabilizer (225), which typicallyalso creates a downforce, considerably farther aft of the center of mass(203). This greater leverage in prior art allows the size of thehorizontal stabilizer (225) and the amount of downforce to be minimizedfor drag reduction benefit. However, the invention counterintuitivelyenlarges control structure, reducing or eliminating the tail requirementand dividing the required pitch stabilizing function among external,supported elevon structures (9,10) more specifically placed behind thewingtip area; firstly providing the efficient, simultaneous control ofpitch (232) and roll (233) (FIG. 23).

Eliminating tail structure shortens the moment arm providing pitchstability to the aircraft. Other things being equal, this action causesan increase in downforce loading on any newly placed structures, whichhas been a consequence avoided in prior art as it would increase drag.However in the invention, the resulting decalage (the difference inangle of attack between wing and stabilizer) and loading merelyincreases pitch stability, a benefit most notable in turbulence.Although the full-flying wingtip elevon (9,10) of a preferred embodimentof the invention can thus provide stabilizing counterforce (231) andexemplary control whether positioned anywhere from below the wing toabove the wing (4), provided its centers of pressure are behind thecenter of wing lift (204), that it has adequate size, and provided thatit creates negative lift by means of inverted airfoil geometry or angleof attack, maximum results in reducing drag occur when it is placedabove the wing (4) and generally above the wing-influenced downflow ofair over the wing. Induced drag benefits decrease significantly if theouter portions of the elevons (9,10) do not reach optimum locationsabove the wing tips, thus the practicer is advised to ensure that theouter tip of the elevons (9,10) are not moved inward (towards thecentral plane dividing the aircraft into left and right sides) by morethan one-quarter of the wing semi-span.

Therefore as mentioned, instead of attempting to deal with the highkinetic energy of vorticular flow by means of small surfaces or small,fast-moving airflows, such as provided by vortex generators, wingletsand other such wingtip devices in the prior art, airfoil structures (9,10, 141, 154) spanning a high proportion of the wing span (4) areutilized to efficiently move enough air mass to gently absorb or opposethe streamwise development of strong vortex from the wing (4), bycreating opposing airflows proximally above the outboard portion of thewing (4). If located behind the center of wing (4) lift, they canprovide this function in their combined capacity as controllableelevons, thereby acquiring a bonus from the pitch stabilizingrequirement while allowing the reduction or elimination of additionalpitch control structure. As a result, equilibrium is reached morequickly in the wake of the aircraft, and induced drag is lowered usingrequired forces rather than introducing new ones.

Where an upwardly extending elevon support structure (5) at the wingtipcan be likewise utilized to provide a required force for control, suchas stabilizing or controlling the aircraft in lateral yaw, it can beloaded to produce directed lift in contribution to stability andreduction of induced drag. However, unlike prior art, function of theupwardly extending elevon support structure (5) as a wing or winglet(FIG. 22B) is not a priority of the invention, and total drag may beminimized by keeping any desired aerodynamic functions to a bareminimum. The generally horizontal arrangement of downforce airfoils(9,10) positioned over or under lifting wingtips may be understood toprovide the primary aerodynamic benefit, especially when controlled bymeans of rotation about a spanwise axis (FIG. 23). Structural benefitsfrom negative loading of the ailerons (9,10) include reducing the rootbending moment of wings if mounted upon the wings, however, making theuse of upwardly extending support structure a carefully consideredvariable.

Operation of these elevons (9,10) in the preferred embodiment of FIG. 23illustrate how principles of synergy employed in the invention achieveyet another novel combination of drag-reducing and control-enhancingbenefits from required control forces in flight. Relative to thedirection of fluid flow, as disclosed previously, the elevons (9,10) innormal flight encounter the air at a typically negative angle of attack,providing downward aerodynamic force (231). When roll is initiated, theaction of the elevon (10) located on the rising wing (4) of the aircraftis to reduce its negative angle of attack, reducing drag and downforceon one side of the aircraft. This wing (4) is thereby accelerated andlifted, rather than slowed and lifted as in prior art; whereas theopposite elevon (9) increases angle of attack, desirably andsimultaneously increasing aircraft pitch, elevon downforce, andfavorable drag in yaw. Testing of a variety of embodiments hasdemonstrated that the invention consistently produces turns that areexceptionally well coordinated in all three axes with a single turninput, just like steering of a well designed motorcycle is accomplishedby leaning. Adverse yaw is eliminated.

Furthermore, any increase in the aerodynamic loading (204) of theprimary wing (4) in turns (FIG. 23) is accompanied by an increase incounterforce (231) from the elevons (9,10) in maintaining the increasedpitch, thus uniquely moderating the drag increase that usually comeswith maneuvers. Downward loading of the horizontal stabilizingstructures (9,10,141, 154) also adds to the wing loading of the aircraftin flight, with corresponding benefits in speed, stability, ridequality, and reduction of apparent dihedral. These behaviors assist theaircraft of the invention to retain kinetic energy through turns to aremarkable degree, a highly desirable trait for racing aircraft inparticular. (FIG. 9A) Further explanation of the fluid dynamic processesresponsible for the drag reduction benefits of this structure aredisclosed following.

Some practicers of the invention might desire to minimize the span andarea of the elevons, or to reduce their chord, in pursuit of lowersurface drag. However, a best mode practice is disclosed wherein thespan of the elevon (9,10) elements, relative to the wing (2,4)semi-span, is divided so as to employ the “extreme and mean ratio” ofapproximately 0.618 to 1. Such spans assure that the elevons (9,10)create adequate force with minimum drag. Since the elevons (9,10) mustretain sufficient authority to overcome high pitch moments at low speedsand high angles of attack; and at high speeds, without stalling;preferred embodiments will tend to lead the studied practitioner back tosimilar forms disclosed.

Best practice requires that the span, loading, and support of the elevonstructures (9,10) conform to the specific teaching to obtain the fullbenefit offered by the invention for minimizing induced drag regardlessof their position above or below the wing. However, the reader isreminded that induced drag reduction is only one of many beneficialresults obtainable in use of the invention, and that it may not have toppriority in every embodiment. Such excellent control is provided, andsuch efficiency is abundant, to allow the practicer wide latitude inimplementation for particular goals, such as shorter takeoff and landingdistances or very high speed flight. Nevertheless, the requirement forthe elevon structures (9,10) to produce a downforce opposing the lift ofthe wings must not be subverted, as an unsafe and unstable loadingcondition would then exist. Some aircraft may require additional forwardballast or other measures to ensure that the center of lift remainsappropriately behind the center of mass at all times, thus assuring thatthe stabilizers (9,10) are not tasked to create a typically positivelift.

Since no truly similar configuration exists to establish a designationfor an aircraft having separate elevon, aileron, or stabilizer controlsurfaces supported away from the wingtips so as to provide downforce andfull authority for the aircraft in roll and/or pitch; thereforehenceforth I shall designate this configuration “double box wing”. Thisterm is intended to be convenient, rather than a limiting description ofappearance, since while a majority of preferred embodiments present thevisual consistency of a double quadrangle in front view, the inventionis equally enabled by structures which locate controlling elements ofthe claimed arrangement without vertical end support (5). FIG. 16Bembodies the invention in a configuration best described as T-wing. Asimilar alternative would merely stop the wing (4) at the upwardlyextending elevon support (7). Small aircraft (FIG. 15) may particularlyembody the invention wherein the elevon structures are cantilevered(154), or partially cantilevered (152) from the fuselage, as long asthey are able to reach out to the wingtip area and are sufficientlystrong and rigid, as in the embodiment of FIG. 15. This embodimentutilizes a rearward-swept lifting wing (4), which places the center oflift behind the center of mass, and a slightly forward-swept downforcewing (154), which together enable the prevention of stall in accordancewith the method that follows. The reader is reminded that in suchbiplane- or boxplane-like embodiments, the forward, lower wing (2,4)carries the entire weight of the aircraft, plus the download from thewinglike elevon structure (154) exerting negative lift; and that sweepand/or dihedral may be employed to obtain the stall prevention methoddisclosed; both of which stand in contrast to visually similar priorart.

Additional surface drag and additional wetted surface area areconditions usually avoided by the skilled aircraft designer. In order toachieve a net reduction in total drag, drag of the additional structures(5,7) supporting the control surfaces (9,10) must be minimized andbalanced by reductions in control surface drag and fuselage drag asdisclosed. However, the drag of unbroken, optimized foil structures(2,4,5,7,9,10) themselves can be quite low. Such drag is readilyaccepted when balanced by lower induced drag, such as in the design ofsailplanes with very long wings. Many sailplanes are capable of veryhigh speeds and very low total drag. Regarding the structures common tothe invention as serving a similar function to the wingspan of asailplane helps the practicer of the invention see efficiency (and,effectively, a high aspect ratio) rather than simply more surface drag,in enabling structures. Having eliminated the requirement for a longmoment arm to oppose positive pitching moments in level flight, theinvention (FIG. 3) rewards shorter, wider, area-ruled fuselage (1)designs and shorter boom (6) designs having reduced Reynolds number andviscous drag for a given volume. Coupled to propulsion designs thatrecover boundary layer drag from the fuselage, (FIG. 1, FIG. 11) thepracticer of this invention is empowered to achieve previouslyunattainable results in the reduction of total drag.

The light weight of structure possible in the invention because ofcontrol simplification, shorter fuselage, and other factors enablesfurther novel use of the configuration disclosed. Whereas certainpracticers of the art are desirous of variable wing geometry methods,and whereas the use of boom structure (6), fuselage structure (1) finstructure (7) or other supportive structure in the vicinity of the wingroot area (3) provides a natural change in wing thickness, thereby theconfiguration common to the teaching may be better adapted to retractingand extending wings than other designs. Attachment between the elevons,elements of supporting structure, and wings may be rotatably connectedto allow controllable articulation of individual connections about anaxis of rotation generally parallel to the longitudinal axis (235) ofthe aircraft. Such attachment would allow predominantly verticalelements of structure (5,7) in high speed flight to rotate toward thehorizontal for additional lift capacity at lower speeds, to allowextending or retracting wings, or to change the angle of attackregulated by the stall prevention method described below.

By prescribing a more specific configuration of the elements of theinvention thus described, a method for the prevention of inadvertentstall is disclosed as a further refinement of the invention. As is wellknown to those skilled in the art, at a point when the lifting foilsurfaces of an aircraft (or other body moving through a fluid medium)encounter that medium at a greater angle of attack than that for whichthe lifting foil is capable of producing lift, the airfoil (or otherlifting foil surface) stops producing lift and the airfoil is said tostall. Since stall is a function of the angle of attack rather thanairspeed, a stall can occur under a wide variety of flight conditions,including, but not limited to: turns, during which the lifting surfacesare loaded by acceleration and the angle of attack is increased; lowerair density, wherein the surfaces produce less lift than in a higherdensity medium, resulting in increased angle of attack to maintain adesired amount of lift; and pitch maneuvers, such as when the pilotinitiates an increase in angle of attack for the purpose of gainingaltitude, or for flare to reduce speed and rate of descent at the pointof landing.

Therefore, an object of many inventors has been the effective preventionor prediction of stalls. Canard aircraft (FIG. 22B), in particular, havedemonstrated a method for prevention of main wing (4) stall that isreliant upon stall of the canard (229) prior to stall of the main wing(4). A stall in the canard (229) allows the aircraft nose to drop, witha corresponding increase in airspeed, which drop reduces angle of attackand allows canard (229) recovery. Feedback, in the form of bobbing ofthe aircraft nose as this process occurs, further alerts the pilot tothe onset of stall conditions. Canard aircraft are highly regarded, yetsimilar stall performance—without the canard—has largely remainedelusive. Additionally, studies have shown that the configuration thatoffers lowest total drag is not canard (FIG. 22B), but rather aft-tailedaircraft (FIG. 22A).

When an aircraft is configured per the preferred embodiment of FIG. 1,the reader skilled in the art will recognize that it comprises asuperior method to achieve the long-sought goal of stall prevention, andthat it provides exceptional control of an unstalled, partially stalled,or even fully stalled wing (2,4). FIGS. 18 and 19 show this embodimentfrom the direction of flight at a high angle of attack, and FIG. 20illustrates the action schematically. Since the large elevons (9,10)must exert substantial downforce to achieve or maintain a high angle ofattack of the wings (2,4) shown in FIG. 18, further increase in theangle of attack of the wings (2,4) must be initiated by an increase inelevon downforce. However, at angles of attack sufficient to create astall condition on the main wing (2,4) (FIG. 19), the inboard portionsof the elevons (9,10) are blanketed in the streamwise flow by theinboard portions of the wings (4). Being thereby deprived of freestreamair in which optimum lift forces are created, that portion of elevon (9)closest to the fuselage, having the greatest moment arm to effectchanges in pitch, begins to suffer a loss of lift, such that the elevons(9,10) maintain authority but cannot increase the pitch further. Theprecise angle (205), relative to the longitudinal axis of the wingchord, for positioning the inboard elevon (9,10) surface may be chosento intentionally limit the ability of the aircraft to achieve angles ofattack (201) that result in stall (FIG. 20). While in this position ofhigh angle of attack (201), the elevons (9,10) outboard of the area ofblanketing and interference remain in freestream air (202) and maintainfull authority to roll the aircraft and to initiate downward pitch inrecovery of normal flight attitudes. Additionally, that portion of theflight control surfaces being buffeted by turbulence sends tactilefeedback to the pilot through the controls that a specific angle ofattack (201) has been reached, regardless of airspeed or othermisleading and irrelevant information. The aircraft will also thentypically exhibit similar nose bobbing associated with the stall ofcanard designs, although for entirely different reasons. So informed,the pilot or automated flight control system is empowered to completelyprevent unintentional stalls.

Sometimes stall is a design element. Aircraft which do not normallystall also cannot be intentionally flown at speeds below stall speed, orcontrollably descend at high approach angles and rates of descent thatare below stall speed. However, the invention, when optimized for such,provides control that allows certain embodiments to be flown at very lowspeeds in a fully controlled manner. Aircraft may be designed that arecapable of controlled descent at high angles of attack or deep stall,such that extremely short landings may be conducted at high angles ofapproach but at low rates of descent and low airspeed, promoting greatersafety at the least and greater utility as an object. The requiredcontrol deflections to effect this behavior in various embodimentstested are substantially less than required by prior art, and as aconsequence of the size, placement, and operational characteristic ofsurfaces disclosed herein, transition to and from such deep stallcondition is a smooth and predictable nonevent. Stall recovery maylikewise occur gracefully. Certain embodiments have shown potential todescend steeply under full control in a parachute-like glide, yettransition to normal landings. With power on, slow and stable flight atspeeds well below normal “stall speeds” can be performed. Consequently,novelty and utility exists for this unconventional configuration in thatsuch capability exists within a reasonable range of flight controlinputs and with greater safety and authority than prior art.

Whereas the canard configuration (FIG. 22B) causes stall of the pitchcontrol surface (229) in obtaining stall prevention, temporarilyrendering the control surface ineffective, proper use of the inventionensures that the outer majority of the elevons (9,10) do not stall priorto the main wing. Indeed, it may be observed that an increase in wingangle of attack is accompanied by a decrease in elevon angle of attack(FIG. 20), which behavior enhances pilot authority under stall andnear-stall conditions. While both a properly designed canard surface(229) and the elevons (9,10) of the invention must carry similar totalaerodynamic loads, the canard (229) of a canard aircraft (FIG. 22B) is asmaller, highly loaded flight surface having intentionally limitedauthority. Problems with rain or surface contamination, which can causecertain canard aircraft to fall catastrophically below minimum canardlift requirements, are less likely in the double box wing configurationsince the downforce pressure (231) exerted by the larger elevons (9,10)in level flight is a small fraction of their total designed authority(FIG. 23).

Due to the location, size, and number of vertical or inclined stabilizerfoils (5,7) found on the preferred embodiment of FIG. 23, together withrudder (7) travel limits, center of mass (203) placement, and fullthree-axis authority under most stall conditions, resistance to bothupright and inverted spins is characteristic of this embodiment.

In order to achieve the maximum benefit of the method, the position ofthe inboard portion of the elevon (9) should be placed so thatblanketing (FIG. 19) by the leading edge of the wing (4) begins at aprescribed angle of attack (201), chosen relative to the stallcharacteristics of the wing airfoil selected. (FIG. 20) The wing leadingedge, from this point outward, should preferably sweep or curve back ata suitable angle to expose a greater portion of the outboard elevon tothe freestream flow (202). Correspondingly, the elevon should preferablysweep forward from its rearmost position (A) inboard, to its forwardmostposition (B) outboard (FIG. 3). The intent and effect of the method isthat the wing (4) is at a selected, high angle of attack relative to thefreestream flow (FIG. 19), and from this position (205), blocks thefreestream flow (202) over an inboard portion A of the control surface,whereas the outboard portion B of the control surface, being at agreater angle (205) to the wing (4) than the angle of attack (201) isnot so affected, and such that a gradual disruption due to winginterference is taking place at the elevon (9). (FIG. 20)

Although a combination of wing anhedral and elevon dihedral provides analternative to sweep within the method, it should not be the object ofdesign to sacrifice combined benefits of the invention merely to obtainthe method regarding stall prevention. Wing (4) and horizontalstabilizer structures (9,10) should remain generally horizontal.Moreover, the height of the stabilizing control surfaces (9,10) abovethe wing (4) may advantageously be considered subject to wing semi-span(2-4) for optimum reduction of induced drag, and a best mode of practiceis disclosed wherein the height is approximately 25% of the wingsemi-span provided that the result remains above the generallyinfluenced wing airflow. However, variation in this height is acceptableand relates directly to the angle of attack (201) being regulated (FIG.20), and to wing chord with respect to the stall prevention method andthe airfoil section characteristics.

DESCRIPTION OF PRIOR ART

U.S. Pat. No. 1,971,592 to Zaparka discloses aileron control surfacesdistinct and separate from a wing which are configured to affect theflow over a substantial portion of the wing airfoil, being substantiallylocated in the downflow over the wing. Unlike the present invention,this prior art is taught for aircraft having the usual stabilizer andelevator tail surfaces. It is therefore important to understand thatthis early prior art and the present modern invention are poorlyrelated. Functions of each are opposing in nearly every respect,especially with regard to mode of operation: an aileron as taught byZaparka is dangerous to the present invention, and the present inventionapplied to the prior art would likewise render it unsafe anddysfunctional. For example, as specifically disclosed, and referenced inall claims, a central objective of this prior art is to affect theairflow over the wing airfoil in order to increase the lift coefficientof the wing airfoil, which is quite opposite to the operation of thepresent invention. These positive-lifting ailerons of prior art aretherein shown to produce a variable positive lifting force, bothindividually and in tandem with their mutual effect upon the wings, byassisting the attachment of flow over the wing. In the prior art,operating the ailerons to produce force opposite to wing lift causes anundesirable separation of wing airflow. This is an easily anticipatedresult, because the distance from the ailerons to the wing at their mostdistant exemplified placement is only approximately one-fourth of thewing chord length. In apparent response, the prior art teaches afloating aileron able to self-adjust to downflow in avoidance ofnegative lift and resulting airflow separation, yet, as in all claims,requires that the aileron remain substantially in the downflow over thewing.

For objectives not found in prior art, the present invention exclusivelyteaches negative lift from much larger and much more separate airfoilscrucially positioned outside of, and spaced away from, thewing-influenced downflow as defined by Zaparka. Separation required bythe present invention is typically many times greater than even the mostseparate placement claimed therein. In addition to teaching aileronsspaced at a distance sufficient to cause an independence from wingdownflow, the present invention centers attention on the results ofindependent aileron action not in combination with the wings, and uponan opposite use of lift and drag in creating yaw. Further, the inventionimproves upon prior art by use of widely separated, larger externalairfoils not only as ailerons but also as downforce elevons (9,10) forpitch stabilization and control, preferably along with elimination ofconventional stabilizer and elevator surfaces. Unlike prior art, thesesignificant improvements have little to do with lift enhancement, butrather, much to do with drag reduction and efficient control. The aboveapplies equally to other similar art, such as Junkers flaps.

U.S. Pat. No. 3,834,654 to Miranda teaches a boxplane (boxwing) aircrafthaving certain similarities in appearance to some embodiments of thepresent invention. However, any resemblance is superficial. Box-wing andjoined-wing aircraft of the prior art are canard or tandem wing designswherein both lifting surfaces, fore and aft, are always arranged toprovide substantial positive lift. None of them would fly if thesecondary wings exerted substantial downforce in normal flight. Inaddition, since the disclosure of this and similar inventions, numerousattempts have been made to develop aircraft according to the teaching.As a result, a fundamental flaw has been observed; tandem wing aircraftare susceptible to unrecoverable conditions caused by loss of lift onthe rear wing and to stability problems due to tandem loading.

U.S. Pat. No. 4,146,199 to Wenzel, regarding a biplane joined-wingaircraft having a lifting fuselage, well illustrates the factorscomplicating stability for aircraft that resemble my invention but whichdo not stabilize the aircraft in pitch by means of rearward airfoilsproducing downward force rather than positive lift. Such aircraft arehighly susceptible to spins and stalls. As in all joined wing and boxwing prior art, the rearward wings of this prior art provide positivelift. Therefore, despite a few visual similarities, no prior art isfound relative to the present invention as a whole.

As should be expected, much prior art is found relative to variousmethods for reduction of induced drag which are unrelated to the presentinvention. The majority of such art has focused primarily upon thedesign of wings and to improvements thereto. By contrast, this inventionis not concerned with wing or winglet designs, wingtip apparatus,joining structure, or the continuity of vorticular flow. Much prior artdirects emphasis to the attempted control of symptoms, rather than theircause. Drag sources critically targeted in prior art—such asdiscontinuity, shed vortices, and interference—are well tolerated in theinvention disclosed herein, since, as in all aircraft, many flowphenomena occurring at the wings are powered by the energies previouslyimparted to their wake, and this invention minimizes such energies, muchas ground effect reduces vortex phenomena for conventional aircraft.While the invention offers lower induced drag in providing multiplebenefits relating to multiple efficiencies, its practice should not beunderstood as limited to embodiments having drag reduction as theprimary priority, nor constrained by unrelated teachings found in priorart, which is frequently defective. Thus, although the configuration ofthis invention a offers wide variety of options which tolerate manycommon methods for the joining and filleting of the airfoil surfacesand/or other supporting structure when (and if) it is used, none isherein specified.

While the principle of the invention is made clear in the illustrationsand embodiments shown and described, it is immediately recognized bythose skilled in the art that many modifications are possible and may bemade within the scope of the present invention for the specificapplication and need of the practitioner without departing from thespirit of the invention disclosed, and the invention includes all suchmodifications. Therefore, in view of the foregoing and in accordancetherewith, I claim this invention with all rights reserved.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an aircraft having a single engine driving a propeller (8)in the so-called pusher configuration; comprising a large fuselage (1)with capacity for at least six individuals and baggage; designed forlong range high speed operation with achievable STOL capability. Theaircraft has a swept, low wing lifting foil structure (4); upwardlyextending elevon support structure (5) at the wingtip; forward sweepingelevons (9,10) pivotably attached at their ends, comprising twocontrollable airfoil structures providing downforce; their inboard endssupported by inclined vertical stabilizers (7) attached to short booms(6) extending from the wing root/removable wing panel (4) junction (3).The wing root (2) is thick and of large chord in order to effectivelytransfer flight loads; including in particular torsional loads; tofacilitate removable wings, retracting landing gear, and to accommodatefuel. This aircraft is a preferred embodiment designed by the inventorand is called Exponent. As in a majority of embodiments, compositeconstruction is used extensively.

FIG. 2 shows the aircraft of FIG. 1 in front view and the direction oflift provided by the arrangement of lifting foil structures in normalflight. Loading of the elevons (9,10) is downward and generatesapproximately 6% to 12% of the aircraft weight at an angle of attackselected for minimal drag. Landing gear (21) attachment is beneficiallylocated in an area of structural advantage and may be retracted. Allstructure outboard of landing gear (21) may be removable and/or foldableto promote roadability, transportability, and storage. A significantpercentage of drag losses due to boundary layer fuselage (1) frictionare recaptured by the wake-immersed design of the propeller (8).

FIG. 3 shows the aircraft of FIG. 1 in top view. Outboard wings (4) areswept at 137.5 degrees of included angle at a reference chord position.Fuselage (1) loading provides for favorable balance with a large rearengine (31) and two persons seated forward. Additional payload adds toforward movement of the aircraft center of mass for appropriate handlingunder increasing weight. Fuel, and up to one half of payload, is carriedat center of mass at the wing root (2). Section lines A-A and B-B areindicated referencing the sectional views of FIG. 20.

FIG. 4 shows the aircraft of FIG. 1 in side view. Vertical stabilizerfoil structures (7) having rudders and speed brakes provide lateralstabilization behind the center of mass. Propeller (8) tip noise ismoderated by the presence of this structure (7) immediately to eitherside. Elevons (9,10) provide downforce above and behind the wing (4)such that the outboard ends are less behind the wing (4) and the inboardportions are more behind the wing (4). This relationship enables theclaimed method and is illustrated further in FIG. 20. Steerable nosegear (22) retracts into the fuselage (1).

FIG. 5 shows the invention applied to an aircraft of similar size to theBoeing 747, having a larger fuselage (1) with two decks. The inventionallows for an increase in wing area and a reduction in wing twist(washout) with numerous benefits. A reduction of conventional wingcomplexity is advocated as an attainable object of the invention.

FIG. 6 shows the aircraft of FIG. 5 from the front. Rudder structure (7)combines with pylon structure (52) for the support of elevons (9,10),supporting engines (51) closer to the aircraft centerline to provideenhanced lateral stabilization and control in conjunction with outboardrudders (5). Engines (51) shown above wings may also be fuselagemounted.

FIG. 7 shows the invention applied simultaneously to a seaplane and to alifting foil hydroplane (71) used to assist the seaplane on takeoff.This embodiment further displays a wing root (2) having negative sweep,an advantageous solution allowing the claimed method when wing sweepwould otherwise place the center of lift too far aft (see also FIG. 21).

FIG. 8 shows the aircraft of FIG. 7 from the front. The high wingconfiguration of aircraft can benefit as readily as the low wingconfiguration from the invention, as the apparent dihedral of theinvention is lower than that of a wing (4) having winglets (5) ofsimilar height (FIG. 22B). For amphibious aircraft, overcoming the dragof water while accelerating to takeoff speed is key, and the novelarrangement of controllable foils disclosed achieves equally improvedeffect in water, as fluid dynamic similarity is well understood by thoseskilled in the art. The improved hydroplane (71) is thus able to providesubstantial lift with minimal drag at lower speeds than the wings,thereby lifting the aircraft free of water drag to better enableacceleration to flight speeds.

FIG. 9 shows an aircraft having a forward engine (31) configuration forhigh propeller (8) efficiency, such as may particularly be advantageousfor racing aircraft. Other, twin engine, racing aircraft are especiallyable to exploit the invention when engines are aligned with twinfuselage booms in the manner of the P-38 aircraft.

FIG. 10A shows an efficient double box wing biplane, configured per thedisclosed teaching for negatively loaded, full-flying, external,supported (7) wingtip elevons (9,10). It should also be noted that allembodiments illustrated are aerodynamically capable of fully controlledinverted flight, but that the disclosed stall prevention method appliesonly to positive G maneuvers. FIG. 10B shows the aircraft of FIG. 10Afrom the front.

FIG. 11 shows the invention as a fighter-style aircraft, havingunobstructed canopy space (112) ahead of wings (4) and engines (31).This embodiment offers the pilot and passengers excellent visibility andfeatures wake-immersed ducted fan propulsion capable of recoveringfuselage drag when properly designed. Duct structure (111) shown maythereby be useful in support of elevon (9,10) structure. The exceptionalmaneuverability and energy retention typical of all embodiments of theinvention makes their flight ideally suited to high performance sportaircraft, regardless of propulsion. Military aircraft can be expected tofully exploit the invention in similar manner.

FIG. 12 shows a twin engine business jet embodiment having boomstructure (6). An increase in wing area and total aspect ratio (togetherwith a decrease in apparent wing aspect ratio) improves handling,strength, and fuel storage over prior art while reducing runway lengthrequirements.

FIG. 13 shows an aircraft having multiple fuselage bodies (1) serving assupport structure. The invention allows such enormous aircraft tomaximize wing area without a large penalty in induced drag, and furtherenables realistic use of central wing (2) and fuselage structure forpassengers, cargo, freight, and fuel. Since wing span is a constraininglimit to very large aircraft, the invention represents a realisticsolution to enable their further development. Control featuresincorporated into the wings (2,4) may be considerably less extensivethan required in prior art.

FIG. 14 shows an aircraft having a boxplane-like configuration, butwherein the controllable upper horizontal stabilizer structure (141)exerts a generally negative downward force in level flight. In smalleraircraft of the same arrangement (FIG. 15) suitable supporting structureto enable the invention may consist solely of at least one inverted,cantilever elevon structure (154) providing downforce, whereas largersimilar craft may require supporting struts (152) or outboard wingtipstructure (143). Opposing lift and opposing vorticular flows from theflight surfaces reduce streamwise vortex development, maintainingbenefits of the invention over prior art in either case. However,diminishing benefits are realized as the span of the control structures(141,154, 9,10) is reduced below the wingspan, therefore the practiceris advised to maintain an upper structure span close to that of wing (4)span to keep the control surfaces substantially above the end of thewing (4). As in all embodiments, the airfoils providing downforce mustremain spaced from the wing-affected downflow. Although not havingfull-flying elevons, cantilever biplane-like embodiments such asillustrated in FIG. 15 represent a particularly pure and excellent formof the invention.

FIG. 16A shows a twin engine (31) aircraft of conventional typereconfigured to employ the invention. Elevons (9,10) are swept forwardto allow outboard portions to remain in freestream air at high angles ofattack while improving their stability. Aircraft having lesser wingsweep may thus incorporate the method for the prevention of stall.

FIG. 16B shows a twin engine (31) aircraft wherein the pivotable elevons(9,10) are centrally supported (7) and maintain independence fromwingtip support structure. Aircraft supporting unswept elevons (9,10) inthis manner benefit from a rearward sweep and/or anhedral (negativedihedral) of the main wing (4) leading edge to incorporate the stallprevention method. Further, the location of the support structure (7)can also be placed at or near the wingtip in claimed embodiments. Thisconfiguration of the invention begs the designation T-wing.

FIG. 16C shows the T-wing embodiment in front view. Vorticular flow(161) from the elevons (9,10) opposes that of the wing (4) outboard andthat of the propeller (8) wash inboard for drag improvement over priorart.

FIG. 17 shows the invention applied to a blended wing-body (BWB)aircraft. Rethinking BWB designs in light of the invention opens manydoors to innovation, since maximum wingspan is not required for induceddrag reduction, whereas optimal wing loading along with improvedstability and control remain primary obstacles to the greater success offlying wing aircraft. In this embodiment, structure (7) supporting theelevons (9,10) at their inboard locations provides highly desired yawstability, as do wingtip structures (5). Shorter, more highly loadedwings (4) may be built without the characteristic twist of typicalflying wings, and using positive pitching moment airfoils; againimproving efficiency.

FIG. 18 shows the aircraft of FIG. 1 from upstream of the relative windat a high angle of attack. Elevons (9,10) are at a relatively lower(negative) angle of attack than the wings (4) and remain in freestreamair at all times, even if the aircraft is yawed or slipped. Exceptionalcontrol is assured.

FIG. 19 shows the aircraft of FIG. 18 from upstream of the relative windat a critical angle of attack approaching stall. Inboard portions of theelevons (9,10) are no longer visible in the freestream air, and thedownforce required to maintain the high angle is borne by the outboardportion of the elevons. Loss of downforce caused by blanketing of theelevons (9,10) by the wing (4) causes the angle of attack of the wing(4) to be lowered, averting main wing stall.

FIG. 20 represents the condition of FIG. 19 in two simplified sectionalviews A-A and B-B, which reference the section lines shown on FIG. 3.Referring to Section A-A, at a selected high angle of attack (201), theprimary wing (4) blankets the freestream flow (202) over the inboardportions of the stabilizer control surface (9), depriving it offreestream flow (202) and substituting turbulence, thereby reducing itsability to impart downward force in maintaining a high angle of attack(201) of the wing (4). However, further outboard (Section B-B), at thesame angle of attack (201), outer portions of the elevon (9) remain infreestream flow (202), providing full roll and pitch authority for theaircraft. Placement of the elements (4,9) varies by distance and angle(205), which forms a basis for specifying a desired behavior in thelimiting of stall.

FIG. 21 shows a compact sailplane embodiment of the invention. A shorterwingspan having the same low drag as a conventional, long wingspanallows higher wing loading at a lighter weight, improved structuralperformance, and increased speed envelope in addition to advantages dueto size.

FIG. 22A (Prior Art) A conventional low wing aircraft is shown forreference to fuselage (1), wing root (2), wing (4), aileron (221, 227),elevator (225), flaps (222), seams (223), hinge lines (224), andhorizontal stabilizer (220).

FIG. 22B (Prior Art) A canard pusher aircraft is shown for reference tofuselage (1), wing root (2), wing (4), winglet (5), engine (31),propeller (8), aileron (221, 227), canard (229), and elevator (225).

FIG. 23 shows the action of the horizontal control surfaces (9,10) andthe primary control axes (234, 235, 236) of the aircraft of FIG. 1.Wings (2,4) exert lift upward, having a center of lift illustrated forconvenience as bilateral centers of lift (204) longitudinally aft of thecenter of mass (203). This condition creates a nose-downward (positive)pitching moment that must be balanced by downforce (231) from theelevons (9,10) in normal flight. The longitudinal distance from theircenter of aerodynamic pressure (231) to the center of mass (203), andtheir area, weight, and section properties are chosen so that adownforce (231) approximately equal to 6% to 12% of the vehicle weightmay be exerted in trimmed cruising level flight with minimal drag.

I claim:
 1. An apparatus forming an aircraft which is designed forflight by movement through the air, said aircraft having front and rearportions and a center of mass, said aircraft having left and right sideswhen divided by a central plane of reference, said aircraft havingthereby inboard portions closer to said central plane of reference andoutboard portions farther from said central plane of reference,comprising: at least one aerodynamic lifting surface configured toaffect the flow of air near said at least one aerodynamic liftingsurface when said aircraft is appropriately moving forward, said atleast one aerodynamic lifting surface thereby configured to createpositive lift when said aircraft is appropriately moving forward, saidat least one aerodynamic lifting surface thereby forming at least onewing, said at least one wing having a center of lift which is rearwardof said center of mass of said aircraft in flight; at least one airfoilstructure comprising a means for creating aerodynamic force when saidaircraft is appropriately moving forward, said at least one airfoilstructure positioned predominantly rearward of said at least one wingand entirely above said at least one wing, said at least one airfoilstructure having a direction of aerodynamic force generally oppositethat of said at least one wing when compared to said at least one wing,thus providing the aircraft with positive pitch stability when theaircraft is in trimmed level flight, wherein said means for creatingdownward aerodynamic force by said at least one airfoil structure issaid at least one airfoil structure having an inverted angle of attackwhen compared to said at least one wing in trimmed level flight, said atleast one airfoil structure spaced from said flow of air near said atleast one wing, said at least one airfoil structure occurring on bothsaid left and right sides of said central plane of reference, said atleast one airfoil structure having at least one center of aerodynamicforce which is rearward of said center of lift, said at least oneairfoil structure is of sturdy construction appropriate with regard tosaid aerodynamic force, said at least one airfoil structure isadjustable to vary said aerodynamic force of said at least one airfoilstructure to thereby provide at least partial control of said aircraftwhen said aircraft is appropriately moving forward; wherein said atleast one airfoil structure is constructed so as to have outboardportions thereof positioned outward of said central plane of referenceto a distance at least four-fifths of the distance from said centralplane of reference to a tip end of said at least one wing and whereinthe aircraft center of gravity is forward of said center of wing lift.2. An apparatus according to claim 1 wherein the at least one airfoilstructure is spaced from the at least one wing without direct structuralconnection to a fuselage.
 3. An apparatus according to claim 1 whereinthe at least one airfoil structure is mounted upon the at least onewing.
 4. An apparatus according to claim 1 wherein the at least oneairfoil structure is mounted upon the at least one wing and spaced abovethe at least one wing tip.
 5. An apparatus according to claim 1 whereinthe at least one airfoil structure is mounted upon the at least one wingusing a plurality of upwardly extending airfoil supports extending fromsaid at least one wing to said at least one airfoil structure.
 6. Anapparatus according to claim 1 wherein the at least one airfoilstructure has at least one unadjustable portion configured with respectto said at least one airfoil structure.
 7. An apparatus according toclaim 1 wherein the at least one airfoil structure pivots upon agenerally spanwise axis.
 8. An apparatus according to claim 1 whereinthe aircraft may be controlled by means of adjustable positioning of atleast part of the at least one airfoil structure; said at least oneairfoil structure thereby providing at least partial control of saidaircraft when said aircraft is appropriately moving forward.
 9. Anapparatus according to claim 1 wherein the center of mass is behind thecenter of lift when the aircraft is inappropriately loaded.
 10. Anapparatus according to claim 1 wherein the center of mass is behind thecenter of lift when the aircraft is empty.
 11. The apparatus of claim 1,wherein said at least one downforce airfoil structure extendssubstantially perpendicular to said central plane when said apparatus isviewed from the front portion.
 12. An apparatus forming an aircraftwhich is designed for flight by movement through the air, said aircrafthaving front and rear portions and a center of mass, said aircrafthaving left and right sides when divided by a central plane ofreference, said aircraft having thereby inboard portions closer to saidcentral plane of reference and outboard portions farther from saidcentral plane of reference, said aircraft configured with respect to adownward direction and an upward direction, comprising: at least oneaerodynamic lifting surface configured to affect the flow of air nearsaid at least one aerodynamic lifting surface when said aircraft isappropriately moving forward, said at least one aerodynamic liftingsurface thereby configured to create positive upward lift when saidaircraft is appropriately moving forward, said at least one aerodynamiclifting surface having a center of lift which is rearward of said centerof mass of said aircraft in flight; at least one downforce airfoilstructure comprising a means for creating downward aerodynamic forcewhen said aircraft is appropriately moving forward, said at least onedownforce airfoil structure positioned predominantly rearward of said atleast one aerodynamic lifting surface and entirely above said at leastone aerodynamic lifting surface, said at least at least one downforceairfoil structure having a direction of said downward aerodynamic forcegenerally opposite to the direction of said positive lift of said atleast one aerodynamic lifting surface, said at least one downforceairfoil structure configured to create a magnitude of said downwardaerodynamic force sufficient to thus provide the aircraft with positivepitch stability when the aircraft is is in trimmed level flight, whereinsaid means for creating positive pitch stability when the aircraft is intrimmed level flight is said at least one downforce airfoil structurehaving an inverted angle of attack when compared to the at least oneaerodynamic lifting surface in trimmed level flight, said at least onedownforce airfoil structure spaced from said flow near said at least oneaerodynamic lifting surface, said at least one downforce airfoilstructure occurring on both said left and right sides of said centralplane of reference, said at least one downforce airfoil structure havingat least one center of said downward aerodynamic force in which said atleast one center is rearward of said center of lift, said at least onedownforce airfoil structure is of sturdy construction appropriate withregard to said aerodynamic force; wherein said at least one downforceairfoil structure is constructed so as to have outboard portions thereofpositioned outward of said central plane of reference to a distance atleast four-fifths of the distance from said central plane of referenceto a tip end of said at least one aerodynamic lifting surface andwherein the aircraft center of mass is forward of said center ofpositive aerodynamic lift.
 13. The apparatus of claim 12, wherein saidat least one downforce airfoil structure extends substantiallyperpendicular to said central plane when said apparatus is viewed fromthe front portion.
 14. The apparatus of claim 1, wherein the means forcreating downward aerodynamic force by said at least one airfoilstructure further comprises the provision of negative camber relative tosaid at least one wing.
 15. The apparatus of claim 14, wherein said atleast one airfoil structure further comprises a fixed portion and amoving portion, wherein said moving portion can be moved relative to thefixed portion to vary the said at least one airfoil structure's camberand angle of attack.
 16. The apparatus of claim 12, wherein the meansfor creating downward aerodynamic force by said at least one downforceairfoil structure further comprises the provision of negative camberrelative to said at least one wing.
 17. The apparatus of claim 16,wherein said at least one downforce airfoil structure further comprisesa fixed portion and a moving portion, wherein said moving portion can bemoved relative to the fixed portion to vary the said at least onedownforce airfoil structure's camber and angle of attack.